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The present invention relates to high-speed data communications techniques. More particularly, the present invention pertains to a method and apparatus for interleaving and de-correlating data transmitted over a serial data channel so that a burst error within the channel of less than or equal to a specified number of bits can be detected and/or corrected.
High-speed data transmission often occurs on band-limited channels such as multi-mode fiber and backplane links. It is well understood that high-speed transmissions over band-limited links can cause high levels of Inter-Symbol Interference (ISI). In particular, lasers, amplifiers and other components in the data path can limit the analog bandwidth and compound the problems associated with ISI. Band limiting is known to produce a correlation between errors that leads to a localized group of errors that are generally known as burst errors. A burst error is generally defined as two or more bits in error that occur in close proximity to each other. A burst error can contain a run of good bits that are less than, or equal to, the burst window.
High-speed data transmissions are also subject to transmit jitter, near-end crosstalk (NEXT) and far-end crosstalk (FEXT) interference and baseline wander effects that are statistically non-Guassian. These noise and interference sources result in a higher probability of burst errors than in a channel with just white noise.
Coding systems that use error correction can be defeated by the presence of burst errors in a channel. Interleaving is one way of dealing with such errors without the added complexity of multiple-bit error correction codes that are longer than the burst length. Interleaving xe2x80x9cwhitensxe2x80x9d the noise in the channel allowing error correction to achieve coding gain closer to the theoretical limits in white noise. More specifically, interleaving reorders the bits prior to transmission so that a burst error in the channel appears as a series of single bit errors after the receiver applies the reverse interleave function to the incoming data stream.
Interleaving, however, typically requires a new level of synchronization at the receiver to determine the interleave sequence within the received data stream.
It would therefore be desirable to provide an interleave coding and decoding technique that makes burst errors appear as a series of single-bit errors while additionally being self synchronizing when combined with standard frame alignment logic.
A method and apparatus are disclosed for serially transmitting cells over a data link so that any burst error less than a predetermined size within a single channel is detectable and/or correctable. In a preferred embodiment, transmit interleave logic is provided that maps the bits of an input word into predefined bit locations of a plurality of data words to form a plurality of interleaved data words. The interleaved data words are transmitted over a serial data channel. Receive logic is provided that obtains word alignment on the received words and de-interleaves the received words to obtain the original data words input to the transmit logic. By interleaving the bits of a received data word over a plurality of data words prior to transmission over the serial channel, burst errors of n bits or less occurring in a single channel result in n or less single-bit errors in the plurality of data words.
Other features, aspects and advantages of the presently disclosed invention will be apparent from the Detailed Description of the Invention that follows.